1. Field of the Invention
The present invention relates to a technique for processing analog signals, and particularly to a comparing device for comparing analog signals with a reference voltage, a method thereof, an analog/digital converting device for converting analog signals into digital signals using the comparing device, and a determining device used for the comparing device.
2. Description of the Related Art
As an example of a circuit for converting input analog signals into digital signals, a pipeline A/D-converter is known (e.g., Japanese Laid-Open Patent Publication No. 9-275342). The pipeline A/D converter is formed of multiple low-bit sub-A/D converters connected one to another. With such a configuration, the pipeline A/D converter performs A/D conversion in steps, by actions of each sub-A/D converter. Each sub-A/D converter includes multiple comparators for comparing input analog signals with a reference voltage, whereby the analog signals are converted into digital signals.
In recent years, rapidly advancing fields such as image processing, communication, and so forth, require a technique for processing digital signals with higher precision at a higher speed. Accordingly, development of an A/D converter for performing high-speed and multi-bit A/D conversion is being undertaken. However, a high-speed A/D converter requires high-speed comparators forming the A/D converter, leading to increased power consumption of the comparators. Furthermore, in general, such a multi-bit A/D converter requires a greater number of comparators. Accordingly, realizing such a high-speed multi-bit A/D converter demands developing of a technique which enables effective comparison with as small a number of comparators as possible while reducing power consumption of each comparator.